1. Field of the Invention
This invention relates to a stent mounting device and a method of coating a stent using the device.
2. Description of the Background
Blood vessel occlusions are commonly treated by mechanically enhancing blood flow in the affected vessels, such as by employing a stent. Stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway. Typically stents are capable of being compressed, so that they can be inserted through small lumens via catheters, and then expanded to a larger diameter once they are at the desired location. Examples in the patent literature disclosing stents include U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062 issued to Wiktor.
FIG. 1 illustrates a conventional stent 10 formed from a plurality of struts 12. The plurality of struts 12 are radially expandable and interconnected by connecting elements 14 that are disposed between adjacent struts 12, leaving lateral openings or gaps 16 between adjacent struts 12. Struts 12 and connecting elements 14 define a tubular stent body having an outer, tissue-contacting surface and an inner surface.
Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of a therapeutic substance at the diseased site. Local delivery of a therapeutic substance is a preferred method of treatment because the substance is concentrated at a specific site and thus smaller total levels of medication can be administered in comparison to systemic dosages that often produce adverse or even toxic side effects for the patient.
One method of medicating a stent involves the use of a polymeric carrier coated onto the surface of the stent. A composition including a solvent, a polymer dissolved in the solvent, and a therapeutic substance dispersed in the blend is applied to the stent by immersing the stent in the composition or by spraying the composition onto the stent. The solvent is allowed to evaporate, leaving on the stent strut surfaces a coating of the polymer and the therapeutic substance impregnated in the polymer.
A shortcoming of the above-described method of medicating a stent is the potential for coating defects. While some coating defects can be minimized by adjusting the coating parameters, other defects occur due to the nature of the interface between the stent and the apparatus on which the stent is supported during the coating process. A high degree of surface contact between the stent and the supporting apparatus can provide regions in which the liquid composition can flow, wick, and collect as the composition is applied. As the solvent evaporates, the excess composition hardens to form excess coating at and around the contact points between the stent and the supporting apparatus. Upon the removal of the coated stent from the supporting apparatus, the excess coating may stick to the apparatus, thereby removing some of the coating from the stent and leaving bare areas. Alternatively, the excess coating may stick to the stent, thereby leaving excess coating as clumps or pools on the struts or webbing between the struts.
Thus, it is desirable to minimize the amount of coating material that is deposited on the interface between the stent and the apparatus supporting the stent during the coating process to minimize coating defects. Accordingly, the present invention provides for a device for supporting a stent during the coating application process. The invention also provides for a method of coating the stent supported by the device.
The present invention provides an apparatus for supporting a stent. The apparatus includes a mounting assembly for supporting a stent during a process of applying a coating substance to the stent. The mounting assembly prevents the formation of the coating or at least minimizes the amount or thickness of the coating that can be formed on the regions of the stent where the mounting assembly is in contact with the stent.
In one embodiment, the mounting assembly includes a mounting member for supporting the stent and a shield member for providing a barrier between a selected area of the stent and a coating applicator. In another embodiment, the mounting assembly includes a first member for supporting the stent at a first end, a second member for supporting the stent at a second end, a third member connecting the first member to the second member and extending through the longitudinal bore of the stent, and a shield member for providing a barrier between a selected area of the stent and a coating applicator.
In still another embodiment, the mounting assembly includes a shielding member capping over one end of the stent without being in contact with the surface of the stent. In another embodiment, the mounting assembly includes a mounting member for supporting the stent and a shield member supported by the mounting member for creating a barrier between a portion of the stent and a coating applicator. In such an embodiment, the position of the shield member on the mounting member can be adjusted so as to allow a user to modify the area over which the shield member covers the stent.
In yet another embodiment, the mounting assembly includes a first member having a first coning end that can be at least partially inserted within a first end of the stent and a second member having a second coning end that can be at least partially inserted within an opposing second end of the stent, the coning ends being in contact with the ends of the stent. In such an embodiment, the mounting assembly further includes a third member connecting the first member to the second member and shielding members supported by the first and second members for reducing or eliminating the amount of the coating substance that is applied to the first and second ends of the stent.
Also provided is an assembly for supporting a stent during the coating process. The assembly includes means for minimizing or eliminating the amount of coating material that can be applied to a designated area of the stent during the coating process. In one embodiment, the means is defined by a hollow body capable of surrounding a region of the stent without being in contact with the surface of the stent. In another embodiment, the amount of coating material can be minimized or eliminated at the regions where the stent is in contact with the assembly.
The present invention additionally provides a method of coating a stent. The method includes mounting a stent on a support assembly, wherein the support assembly is configured to reduce or eliminate the amount of coating that is applied to the regions where the stent is in contact with the support assembly. The method also includes applying a coating material to the stent for forming a coating.
In one embodiment, the act of applying includes spraying the coating material onto the stent. In another embodiment, the act of applying a coating includes applying the coating material to a stent while rotating the stent about the longitudinal axis of the stent. In another embodiment, the act of applying a coating includes applying the coating material to a stent while moving the stent in a linear direction about the longitudinal axis of the stent.